I don't think it is hard, I guess everybody is very focused atm.
1. Game Design:
To me, it's about making the whole game coherent. If you're doing something supposed to be a rogue-like, it should definitely be hard. It is very complex to answer this as it will be very specific to each game style that will be released.
2. Fun:
Entertainement for sure. Pretty close to Game Design btw, if the rogue-like is easy then it won't be fun (to get the same example).
3. Innovation:
Want to be surprised about the mechanics of the game. Could be something already existing but transformed, or brand new mechanic but I agree, this part is hard.
4. Theme:
Well, just lie. I mean, hide stuff, lie about stuff, but don't make it too obvious.
5. Graphics:
Not the most important part BUT I do like to see polished and completed arts. I do prefer a single scene game proto that is looking finished than 10 scenes with crappy designs and animations. It helps the player feeling good in your game.
6. Audio:
It just need to fit the theme. Doing 2D pixel art? Do 8-bit music. Click a button? Wanna hear it.